Astronomy Cast Ep. 806: Mission Tech Series: Thrusters

Welcome to Astronomy Cast

0:00It's the 365 Days of Astronomy podcast, coming in 3, 2, 1.

0:30We'll be right back.

1:00Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I'm Frisier Cain. I'm the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hello, Pamela.

1:30Hello, and this is, for me, the last episode I'm going to record from this location until at least December. Our next two episodes will be recorded with me at home, with you at home, and then we're both off to Japan. Right, and so hopefully we'll be able to record an episode together. Yes. And hopefully the MMX mission won't have launched yet, so we can cover it from Japan. That would be amazing. That would be super cool. I hadn't thought of that.

2:02So MMX is the Mars Moon's Explorer. It's a JAXA-led mission that is going to have the first wheeled vehicle in that low gravity of an environment. Oh, I didn't even think about that. Yeah. So, I mean, yeah, they're going to put a rover, a lander, a hopper. They're going to be exploring. Yeah, folks are going to throw everything at it. Yeah. Yeah. And collect samples and bring them home, and we are here for it. But that's all we're talking about.

Cold gas thrusters

2:32Today, we continue looking at space exploration technologies. And this time, we will examine thrusters, which can reorient a spacecraft and help it maneuver in space. It's maximum flexibility, but you need to bring along some propellant.

2:46Yeah. So, I mean, when I think about thrusters, and my experience with this is like a Kerbal Space Program, where you are building a spacecraft, and you're building the rocket, and you put on the atmospheric rocket bells. Yeah. And you put the vacuum thrusters on, and then, because you are going to need to maneuver around, you put on some maneuvering thrusters. And there are these little bell-shaped objects that are in three directions,

3:16and you bolt a couple of these onto the sides of your spacecraft, and then that allows it to move in various directions. But, I mean, like, can I just say maneuvering thrusters are little rockets, and then we just wrap up the episode, and we go home? Not quite. Okay. I mean, it's slightly more complicated than that, and also gets into the, oh, no, that was bad for the environment factor of space flight. So, the thing about thrusters is you have to be able to turn the suckers on and off.

3:49Right. So, with solid rocket boosters, which you strap on to your rocket generally, you turn those on, and they go, go, go, go, go, go.

4:02With your normal liquid-fueled rocket, you have the oxidizer, you have the propellant, and they mix, and you go, go, go, go, go. With thrusters, you don't want to have to have two tanks, you don't want to have something you can't turn off. And so, they do this in two different ways. One of them is what they call a cold gas thruster, and that is a bit of a misnomer,

4:33because the version of this that all of you are probably most used to is a balloon let go that goes flying across the room. So, you have something under pressure. You have a small opening, and when you go from zero opening to small opening, gas escapes, and as gas goes in high velocity in one direction, whatever it is, balloon or spacecraft, goes in the opposite direction. They actually design these for kids that are super cool,

5:05where you can get a plastic rocket that you fill with water to a certain point, and then you pump with air. Right. And so, you end up with pressurized air, yeah, above the water. Yeah. And when you release the cap at the end, it sprays water and takes off as the pressurized air pushes the water out with extra force. And is this, like, have you, the ones I've seen, they're like a conversion kit.

5:36Like, you buy, like, a two-liter bottle of pop, or a one-liter bottle, whatever's the size. Yeah. And then it's got a pump, like a valve for replacing. It's like a baseball pump, basically. Yeah, exactly. And then a way to replace the valve on the, at the end of the two-liter bottle, and maybe some cool little rocket fins. Yeah. And then you can pump this thing up, and then you can fire it, which is so cool. I don't know if they still make them, but back in the 80s, because we're old,

6:07they had plastic versions that looked like Saturn rockets, complete with fins and everything else, that were, like, the size of a glass Coke bottle, essentially, but thin red plastic. And so it was like you had an actual correct aspect ratio rocket, and they were really easy to get on the roofs of houses. Yes. But they weighed nothing. So unless they directly hit a window at 90 degrees, they weren't going to break anything.

6:40Right. Yeah. Yeah. I'm trying to remember. I had a bottle rocket. Yeah. I can't remember. It feels like it was red. Uh-huh. And it had, like, and then you would fill it with a little bit of water. Yeah. And then you would pump it up, and then you would release it, and you'd fire it up into the air. And it was just the best thing ever. And they'd always tell you, don't pump it more than X times. Don't put more water in it than Y. And, of course, we both probably are guilty of surpassing. Yeah, those are rough guidelines. Come on. Yeah. You've got to push it to the limit.

7:11Yeah. Yes. But it is, like, if you're a parent right now, and you are like, I, you know, my kids are into rockets. My kids are into space. I want cool projects to get a bottle rocket. And they're not going to light themselves on fire, like, with an Etsy's rocket. You've got a cold gas thruster here. Yeah. Yeah. Yeah. So, but that is the underlying technology, which is that you are hurling compressed material out the back of your rocket, and it is experiencing a kick in the opposite direction. It is fun for the whole family. So, that sort of puts your brain in a state to understand what these things are.

7:45And the point being that you let out a little bit of pressure. The material, the gas wants to expand, wants to go out the little hole. Well, your spacecraft experiences a thrust in the opposite direction. This allows you to maneuver, and you put, and you can have, like, the little bells in three different axes. And then you can just shunt the liquid out whichever direction you need. Yeah. And then you get this maneuver in that, in the opposite direction.

8:17And so, that's how they're able to move. Okay. So, you were sort of leading into, there's, like, a bunch of different ways they tackle this, and the cold gas is warm. I do want to add one piece of information, though. Sure. Yeah. So, yes, you could have just three little nozzles. But they do tend to build them in collections of, there will be a collection in this plane, a collection in this plane. Yes. So, if one fails, they are not dead. And you're going to get a rotation, right? Yeah. So, you want to counter it. Yeah. So, often you'll have them, imagine you get your spacecraft.

8:48You've got them on one side and one on the other side, and then you will fire, the thrusters will go off at the same time. Yes. To balance the orientation of the spacecraft. And often, like, when you watch these things firing, it's amazing. They're super cool. Yeah. Because you can see them, and especially, like, animated, like, you watch, like, I don't know. Battlestar Galactica. Battlestar, do they do it? Okay. Yes. I'm sort of thinking about from the Earth to the Moon, or from, or for all mankind. And you can see these little thrusters firing in really quick succession. Like, they only fire for just a fraction of a second, and because, you know, once you

9:22get a little bit of a boost, now you're going to drift in the new direction that you have set. So, you don't have to, you don't have to continuously fire these things. You can do quick little thrusts back and forth. Yeah. Pulseless. Yeah. So, so those, those are your cold gas ones. Um, weird thing that happened this past week. We are recording on October 18th. Uh, there is video of a Tesla Roadster with carbon fiber compressed gas canisters, which

9:56is a really bad idea. Those things explode. They're, they're like the reason we've lost at least one starship. Don't, don't sit next to one. Um, yeah, they're, they're using these cold gas thrusters to do acrobatics with Tesla Roadsters. Yeah, they're doing like a kickflip of a, of a car over a semi truck, or they're doing a, uh, going like a loop to loop, although they've also got a fan that's sucking the car to the track and then they're flipping it around and like, anyway, it's bananas, but

10:29you know. Do not sit next to one. That's all I ask. Right, right, right. Like, they do explode. These are dangerous. Right. So the point just being, I guess if you've seen this, those are cold gas thrusters. Yes. Yeah. Yeah. So Tesla Roadsters have cold gas thrusters. There you go. Yeah. Yeah. So now you feel very knowledgeable about the technology. You've seen it happen to reorient a car. So imagine instead of a car, it's a spaceship. Right, right. Yeah. Yeah. Okay.

Monopropellants and hydrazine

10:57Yeah.

Monopropellants and hydrazine

10:58So, uh, the other way that they build thrusters is with what's called a monopropellant. So earlier you heard me say that with liquid fuel, they have the oxidizer, they have the propellant, they mix, they fire, zoom, you're in space. Um, with a monopropellant and, uh, hydrazine is the most name recognizable form of a monopropellant. You have a big tank or something and a catalyst, typically like metal pellets or something.

11:34And when the liquid monopropellant comes into contact with the catalyst of whatever it may be, a chemical reaction takes place. We don't usually think of it this way, but the catalytic converter in your car is actually causing chemical reactions to remove pollutants from the air that's coming out from your engine. Catalyst means something that causes a chemical reaction. In the case of hydrazine, they are encountering these pellets and suddenly the hydrazine,

12:07which is a big fancy molecule is now five different molecules that are all going, we shall escape now in all directions. And, and so that phase change expansion as it goes over the, the pellets and out through the nozzle is what is then firing your spacecraft. And hydrazine is the most effective molecule we have come up with so far, and it is absolutely going to kill you if you come in contact with it.

12:37Yes. Like the thing that's so important to talk about is just how toxic and poisonous hydrazine is. And there is just an incredible scene in the Martian. If you remember this, this, uh, this part of the movie where Matt Damon is trying to get his hands on water, I think. And he realizes that he's got the hydrazine tanks for the spacecraft and he needs to come up with a chemical reaction that is going to liberate the water out of the hydrazine.

13:07Yeah. And the one he comes up with is fire. Yeah. And so he's inside his habitat, essentially running a flame that is causing a chemical reaction on the hydrazine, which is causing water to drip out. And you know, you've got something that is like deadly, deadly poison. And whenever a spacecraft crashed to earth or whenever there's any kind of problem, it's a huge concern. It's a big cleanup. They've got to do a ton of, of cleanup work and just, you know, any spacecraft that even

13:40returns that has hydrazine thrusters on board, like any of the capsules and stuff, it is the biggest concern. And they are, they have to approach it with toxic protection suits and do a very rigorous cleanup process to make sure that the hydrazine is safe before they sort of get in there and actually work in shirt sleeves. So one of the big things that NASA has been funding in the past few years is research into what they're calling green propellants, trying to find something that approaches hydrazine in

14:15terms of how much thrust it's capable of producing. There's lots of things out there that are monopropellants, just like hydrogen peroxide at 90% concentration, which is going to be, do not touch again, really bad for organics, but hydrogen peroxide, like it encounters UV light and goes, I'm done. I cease to exist. This is why it's sold in brown bottles. So it is a self healing is the wrong word. It is a self eradicating problem.

14:48So hydrogen peroxide at 90% concentration works. It's an option, but it doesn't have the same amount of thrust. They're trying to come up with better things. The research on this is evolving very quickly right now. And a lot of nations, as we're getting more and more spacecraft in orbit that might come out of orbit, um, this is a problem that has to get solved and, uh, we're working on it. That's the bottom line. Right. Yeah. Yeah. Yeah. So, so this is, uh, like, I know the Europeans are working on this as well.

15:21People are looking for other ways to be able to swap out the hydrazine. China's doing a lot of research on this. So, and hopefully they'll get there. Um, but it's, you know, like basic chemistry only, you know, we'll tell you that, you know, there's a limited number of molecules that you can try to get out that'll liberate this and, and, you know, some versions of these are going to be very, uh, very toxic. Is it, is it that it's like super chemically reactive? I forget why hydrazine is so deadly. So, so hydra, it loves to bind with everything that is in your skin.

15:54And it also creates gases like ammonia that are just really not good to breathe. Um, so it's the combination of, it really likes to bond with organics. It breaks down into things that you really don't want to encounter. And so it's either bonding with you or trying to kill you. Right. Yeah. Don't get it like getting your lungs in it. Yeah. Yeah. It's trying to perform chemical reactions with all of your squishy lung parts.

Managing propellant in orbit

16:21It's not good, but I mean, ultimately the idea of having a thruster is once you are in space, they become used. Once you are in space, you are using them to do massive reorientations. These are the things where you're not using your flywheels, where you're not using, uh, everything we talked about in our last episode, this is the, I need to orientate myself 90 degrees really fast, or I need to change my orbit and I'm not changing my, I'm not using massive engines.

16:59So with the SWIFT reboost mission that sadly failed, um, the reason it was necessary is SWIFT was out of fuel to boost itself. And due to how magnificent our recent solar maximum has been, um, every time we have one of those amazing aurora causing solar storms, our atmosphere expands out and puts drag on these spacecraft and SWIFT just seems to be swift enough.

17:31And, um, yeah, so we need thrusters for both massive reorientations as well as for orbital changes. Right. And thrusters are capable of high speed maneuvers that you're not going to get from an ion drive, which is our next episode. And they're capable of these bulk motions that take a lot more energy that you're not going to be wanting to do with your flywheels.

18:01Um, and a flywheel is not going to boost you into a higher orbit. It's just not. Yeah. And there've been examples where say the, the flywheels on a spacecraft have failed and then they continue the science, but now they're just having to use the thrusters on board to, to reorient the direction until they're out of propellant. But when you get to the, you're having to use propellant mode of, of trying to do science operations, you're almost out of time. Yeah. And then the other thing is you get these situations where say the, the upper stage of the rocket fails, you're not quite at the altitude that you need to get to.

18:36Can you use the maneuvering thrusters to give you a little bit of extra Delta V to get you to the place where you want to be in, in orbit? But, but in some cases you can, um, in other cases you can't, like with the link mission that you were just talking about for trying to reboost the Swift mission. Yeah. But you are left with a limited lifespan because you've used this precious propellant. Once it's gone, it's gone. And there's no way that you're going to be able to, uh, you know, you, you, you cannot move your spacecraft without throwing something up overboard.

19:06Yeah. And if you had to use those maneuvering thrusters to finish getting your orbit up, you're out of fuel for all the other reasons you're going to need those maneuvering thrusters for in the future. And so a lot of the times when you think about, say the missions that are at the Lagrange points, they're, they're relying on how, how much fuel that they have in the tank to keep you perched on the L2 point. Once you run out of fuel, the mission is over. Uh, the Gaia mission ended like this.

19:38James Webb will end like this. Even Nancy Grace Roman will end like this. If you're going to go to one of the L1, L2, L3 Lagrange points, it just depends on how much fuel do you have in the tanks? How much, how much do you have in your maneuvering thrusters? And this is one of the modern frustrations of, of doing science from space. There are lots of examples now of satellite trails appearing in Hubble Space Telescope images because Earth orbit is swarming.

20:10And, and so we are having problems from the surface of the planet that are severe, but we're also having problems from orbit of satellite trails in our space images. Um, so you really have to get out to the Lagrange points to get away from other spacecraft. Yeah. Nice clear view of the sky. And then with infrared, you also want to be that far away to not have to worry about all the Earth's thermal heating, uh, issues as you go around and around the planet.

20:41Um, so there's lots of really good reasons to be at a Lagrange point, but we don't presently have developed technology. We have the skillset to build it, but we haven't chosen to build anything that can service anything out at a Lagrange point. And we can't even really, with what you can purchase already designed, we can't apparently service in orbit consistently. We can do it inconsistently.

21:12Um, yeah, I mean, there's been, so both the U.S. and the Chinese have tested out technologies for servicing satellites. Yeah. But generally what that is, is you attach to the satellite like a... You give it a hug. Yeah, like a, like a limpet, like a, you know, a parasite. And now you provide the thruster. Uh, you know, it's like that fish that eats your tongue and replace, and then becomes your tongue, right? So the, uh, you know, the spacecraft are fully operational.

21:44They have run out of fuel in their thrusters. And so the spacecraft can come up and dock with the spacecraft, clamp onto it, and it has fuel. It has maneuvering thrusters. It can then continue the mission. Um, but we're, we're not at the point now where you've got refueling, which would be amazing. Like this is one of the big things is, is, and NASA actually has a, has a experiment on board the International Space Station where they have tested out refueling in space. And I don't know if we're ever going to do an episode on refueling, but it is a, or maybe we already have, I don't know.

22:15But it is a giant issue because you get, um, you know, hydrogen molecules are trickstery, trickstery, uh, and they want to escape. Trixie, that's how you'd say. Uh, and so they want to escape everything. And so it's really hard to hold on to propellant in space for long periods of time. Uh, you know, and so you would imagine some spacecraft... There are other molecules we can use. We just need to... Yes, and hydrazine, for example, right? Um... Methane is a bigger molecule. Sure. But, you know, it's back to that issue. Do you want to ignite? Do you want to bring an oxidizer?

22:47So on and so forth, right? Right. There was this mission.

Future space technologies

22:49One of the other ideas is water, essentially. Yeah. That you could have some mission that is harvesting water from a, an asteroid or a comet, refills its tanks, and then uses solar power to heat up the water, and then you've got a thruster. Mm-hmm. Um, and so a steam-powered thruster. Yeah. Which is very cool. I love the idea that the, the future of, of permanent space exploration could be steam power. It's, it's, we're, we're at a turning point for so many different things.

23:22And one of the reasons that we haven't done a refueling episode yet is we have been one quarter away, one, like, four-month period away, three-month period away, rather, um, from seeing SpaceX do on-orbit refueling between a pair of something on a Starship for years. Years now. Yes. Any day now. This technology has to be figured out in order for the Starship, uh, human landing system or human lunar, I, whatever HLS stands for, um, to get to the surface of the moon.

24:05And Dustin over at Smarter Every Day did such a good video on how hairy the problem is to solve. We're not touching it until there's facts for us to follow. Right. Because he, he did the video you need to all go watch. Yeah. But that might be an interesting series as well, is to talk about the, the, the different technologies, like orbital refueling, um, I think about laser communication systems. Yes. Like, there's a lot of this technology that is, um, nuclear rockets, just stuff that's right around the corner.

24:37That one's on our list to do. Right. Yeah, yeah, yeah. I mean, maybe we extend, but we'll just talk about the technologies that are right. You know, we've got the stuff that is operational, it's working, it's been going for 50 years. And then there's, there's a bunch of really interesting technology that's just around the corner that has been developed because of these known problems. Right. You know, artificial magnetospheres, centrifuges, things like that, but has not been fully deployed yet. We know these things are going to work. They just have to be tested and tried out and people have to commit resources to make these happen.

25:10And maybe that's an interesting extension to this, this series. But anyway, I rabbit hole. And never load a centrifuge the way they loaded the centrifuge in Hail Mary. Every single person who's ever worked in a lab who watched that scene is going, ah, sabotaging. They need to be balanced. Yeah. They need to be balanced. Yeah. Yeah. So always put things in evenly distributed. All right. Well, we have covered another major chapter in our tour through space exploration technology. What's next week?

25:40Next week is ion drives. Right on. Man, I love ion drives. They do not work the way TIE fighters work yet. Yet. One day.

Patron support

25:50All right.

Patron support

25:51Thanks, Pamela. Thank you, Fraser. And thank you so much to all of our patrons out there on patreon.astronomycast.com who are allowing us to be ad-free and keep paying our team behind the scenes to make us look and sound good. Yeah. So, thank you. In your face, capitalism. Advertisers. Yes. Yes. Yeah. Take that. So, side quest. I get emails. We both get emails almost daily, but I'm the one who reads them, I think, that are like,

26:25hi, we would like to talk to you about advertising with AstronomyCast. Delete. And I just write back, no, remove me from your list. Yeah. Delete, delete, delete. It is so pleasing. Yeah. So pleasing. Yes. So, thank you. Thank you, everybody. AstronomyCast wouldn't be here without the amazing support we get on Patreon. This month, we'd like to thank the following $20 a month and up patrons. Adam Anise Brown, Alan Glass, Alexis, Amy Zhang, Andrew Palestra, Arno DeGroote, Astro Sutz,

26:58Boogie Net, Boldrinet, Burry Gowen, Buzz Parsec, Conrad Haling, Daniel, David, David Rossietter, Diane Philippon, Dylan Gee, Eric Lee, Felix Gutt, Frodo Tannenba, Gerhard Schweitzer, Gordon Dewis, Jack Mudge, Jarvis Earle, Jason Kwong, Jean-Baptiste Lou Martineau, Jeannette Wink, Joe Holstein, Joe McTea, Josh Huggins, Caleb Axon, Katie B, Keith Murray, Kenneth Ryan, Kevin Lyle, Kim Barron,

27:37Laura Kettleson, Mark Thompson, Matthew, shut up, Wesley, Kennard, Michael Atkinson, Michael Kompatera, Michael Purcell, Michael Witchman, Mike Hoosie, Nick Boyd, Olga, Paul D. Disney, Rakesh Chitauri, Red Bar is watching, Richard Drum. There's two pages of you. Must load the second page. Robert Hundle, Roger Isaac, Sergei Manilov, Zegi Kemmler, Space Today, The Lonely

28:13Sandperson, Tiffany Rogers, Tim Goresh, Tom Grant, Travis C. Porco, Vitaly, Wanderer M101, William Andrews, Zacchus Maximus, Zero Chill. And thank you all so much for supporting us and being okay with my bad pronunciation. Thank you. Thanks, everyone. And we'll see you next week. Bye-bye. You are listening to the 365 Days of Astronomy podcast.

28:44The 365 Days of Astronomy podcast is produced by the Planetary Science Institute. Audio post-production is by me, Richard Drumm. Project management is by Aviva Yamani, and hosting is donated by LibSyn.com.

29:15This content is released under a Creative Commons attribution, non-commercial 4.0 international license. Please share what you love, but don't sell what's free. This show is made possible thanks to the generous donations of people like you. Please consider supporting our show on patreon.com forward slash CosmoQuestX and get access to bonus content. Without your passion and contribution, we won't be able to share the stories and inspire

29:45the worlds. We invite you to join our community of storytellers and share your voice with the listeners worldwide. As we wrap up today's episode, we're looking forward to unraveling more stories from the universe. With every new discovery from ground-based and space-based observatories and each milestone in space exploration, we come closer to understanding the cosmos and our place within it. Until next time, let the stars guide your curiosity.